A feed-through (or feed-thru) is a device used to enable communication of some sort through a bulkhead, such as a housing of an electronic module. In applications to which the present invention pertains, the feed-through has a solderable metal body portion that is inserted into a bulkhead opening and secured by reflowing solder into the space between the body portion and the inner periphery of the bulkhead opening. The body portion is provided with one or more axial through-holes that define communication paths through the bulkhead. The communication may be physical (pneumatic, liquid, gaseous or mechanical, for example), optical or electrical. In electrical applications, for example, each through-hole accommodates an electrical conductor, and sealant material in the space between each conductor and the inside diameter of the respective through-hole electrically insulates the conductor from the feed-through body portion and the bulkhead. Many electrical feed-throughs also include a filter component such as a ceramic capacitor coupled between the conductor and the body portion to provide noise suppression in electrical signals carried by the conductor. Other filter elements such as inductors and/or resistors may also be incorporated into the body portion to form various well-known filter topologies.
With soldered feed-throughs, the body portion and the bulkhead opening should be sized so that the solder joint therebetween has a substantially uniform radial thickness on the order of 0.14 mm (0.0055 in.) in order to ensure that the solder joint will be sufficiently durable to prevent cracking and yet sufficiently compliant to protect the feed-through filter components (if any) through repeated thermal cycling, particularly when the bulkhead is a high expansion material such as aluminum. From a processing standpoint, this requires some mechanism for maintaining the body portion centered in the bulkhead opening during the solder reflow process. In the U.S. Pat. No. 4,841,101 to Pollock, for example, a step is provided on either the bulkhead opening or body portion of the feed-through to position the feed-through in the bulkhead opening. However, the step approach requires close tolerances on both the feed-through and the bulkhead opening to achieve a snug mechanical fit; in cases where a snug fit is not achieved, the feed-through is free to tilt in the bulkhead opening before and during the soldering operation, creating undesired thin spots in the solder joint.